The goal of this investigation is to achieve a safe, understandable, and precise means of modifying arrhythmogenic tissue via a catheter during a series of in-vitro tank and in-vivo canine experiments. Catheter mediated ablation of arrhythmogenic cardiac tissue using presently available techniques is, as yet, neither proven safe nor effective - especially for ventricular tachycardia or accessory pathways. One of the principle problems is the high pressure, high velocity shock waves generated from arcing of current during delivery of a standard defibrillator pulse resulting in barotraumatic cardiac rupture in some instances. The other problem with the present technique is poor control of tissue injury. This, we believe, results from poor understanding of the basic electrical factors mediating cell death. The focus of this investigation, therefore, will be on developing a better understanding of what type of electrical pulses generate shock waves and on identifying what electrical factors (i.e., energy, charge and/or voltage gradient) are responsible for tissue injury. A unique high energy, variable current waveform modulator capable of delivering synchronized pulses (singly or in bursts) with amplitudes of up to 50 Amps for periods of 1 microsec to 200msec will provide the means to complete the project. The pulses can be delivered synchronously with each heart beat for indefinite periods. Any shock waves that are generated will be monitored by a piezoelectric transducer capable of recording pressures with rise times as fast as 1.5 microsec for amplitudes of 2,000 PSI. The investigation first will identify in-vitro the optimal current waveform characteristics (pulse amplitude, pulse duration, number of pulses, pulse repetition interval, total bursting time, and duty factor) that will minimize creation of shock waves. The second phase will employ current modulation in a canine preparation to determine the relative effect of energy, charge, and/or voltage gradient on cell death. We expect to make catheter mediated ablation of arrhythmogenic tissue using electric pulses safe, predictable and understandable.